Correlation Between Resilient Modulus, Moisture Variation, and Soil Suction for Subgrade Soils

In recent years, interest in determining the influence of moisture changes on the resilient modulus (MR) of subgrade soils beneath a pavement has increased. This is because the 1993 AASHTO Guide for Design of Pavement Structures recommends using a single MR value. The design MR is expected to account for the seasonal variation in subgrade moisture content. This study was undertaken to evaluate the variation of MR with postcompaction moisture content and suction of selected subgrade soils in Oklahoma. A sandy soil (S-Soil) and a clayey soil (C-Soil) were used for laboratory testing. The C-Soil specimens to be subjected to wetting were prepared by a modified compaction method. The proposed method was expected to enhance the flow of water in a specimen during the wetting process. New laboratory procedures for wetting and drying of specimens were also introduced and were used to establish correlations among MR, moisture variation, and suction. Results indicate that MR-moisture content relationships for C-Soil exhibit a hysteretic behavior due to wetting and drying. A similar behavior was observed for S-Soil. The C-Soil was more susceptible than the S-Soil to moisture variation, as expected. It was also observed that changes in MR values and suction were influenced by the initial (compaction) moisture content.